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Junior high school math solution! ! !
1、y=(8+4×x/50)(2400-x-2000)

=(8+2x/25)(400-x)

=3200+32x-8x-2x? /25

=-2x? /25+24x+3200

2、4800=-2x? /25+24x+3200

x? -300x+20000=0

(x-200)(x- 100)=0

x=200 x= 100

According to the meaning of the question

x=200

3、y=-2x? /25+24x+3200

=-2/25(x? -300 times +22500)+5000

=-2/25(x- 150)? +5000

∴x= 150 has a maximum value, and the maximum value is 5000.